X-ray emitters include an x-ray tube and a housing surrounding the x-ray tube. The x-ray tube itself likewise includes a housing, which is generally embodied as a vacuum housing. Both types of housing typically comprise a soft-magnetic material.
X-ray emitters and especially x-ray tubes are used in a plurality of medical devices, which include, for instance, radiography systems, angiography systems with one or a number of C-arms and computed tomography systems.
The publication DE 19901482 B4 specifies a multiple examination arrangement with a plurality of imaging systems, which are arranged in a room such that a patient lying on a movable patient support couch can be examined in any of the imaging systems without being repositioned, wherein, in addition to a magnetic resonance system with actively shielded magnets, provision is made for an x-ray angiography system with a soft-magnetic casing in the region of the imaging parts for shielding the static stray field of the magnetic resonance system, and the masses of the soft-magnetic casing on the x-ray angiography system are arranged distributed in symmetry with the axis of rotation thereof.
X-ray tubes are sensitive to magnetic fields because the electrons released in the x-ray tube are electrically charged and can be deflected from their path by magnetic fields. Fluctuating magnetic fields which are affected by fluctuations in the magnetic fields themselves or by movement of the x-ray tube through static or dynamic inhomogeneous fields result in a movement of the focal point of the x-ray tube. The movement of the focal point causes the resolution of the x-ray system to deteriorate.
Moreover, magnetic fields emanating from the x-ray emitter, for instance the magnetic field of the anode drive, can also produce interferences in the surrounding objects, for instance EKG cables.
With current soft-magnetic, almost single crystal housings, a definition of the direction of magnetic flux lines through housing walls is not possible.